Paper product and method for manufacturing

ABSTRACT

The invention relates to a paper product and a method for manufacturing a paper product. In an embodiment, the invention includes a paper product including a paper substrate comprising a web of fibers having a first surface and a second surface and having a selective indicator provided over the first surface, the first surface observably different than the second surface under a selective condition. A first release coating can be provided over the first surface or the second surface. In an embodiment, the invention includes a method for forming a paper product comprising applying a composition having a selective indicator to a web of fibers having a first surface and a second surface, wherein the composition is applied to the first surface and results in the first surface being observably different under a selective condition. The method further includes applying a first release composition to one of the first surface or second surfaces to form the paper product.

FIELD OF THE INVENTION

The invention relates to a paper product and a method for manufacturing a paper product. In particular, the paper product can include an optical brightener provided on one side of the paper product.

BACKGROUND OF THE INVENTION

Release liners are products designed to cover at least a portion of another product, such as an adhesive portion of another product, and protect it until the time of use. An exemplary release liner would be the backing on a sticker that is peeled off before the sticker is affixed to something else. Release liners are typically coated with a material, such as a silicone containing material, that provides the surface with desired release properties.

Release liners may be coated with a material providing desired release properties on one or both sides. For example, one-sided release liners are treated to have desired release properties on one side and two-sided release liners are treated to have desired release properties on both sides. For examples of two-sided release liners, see U.S. Pat. No. 6,780,484 (Kobe et al.); U.S. Pat. No. 5,688,523 (Garbe et al.); and U.S. Pat. No. 5,612,107 (Sangani et al.). In some applications, it is useful for the two sides of the release liner to have different release properties. Release liners having different release properties between their sides can be referred to as differential release liners.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary process for manufacturing a paper substrate according to the invention.

FIG. 2 is a schematic view of an exemplary release liner application process. FIG. 3 is a schematic cross-sectional view of a differential release liner in accordance with an embodiment of the invention.

SUMMARY OF THE INVENTION

The invention relates to a paper product and a method for manufacturing a paper product. In an embodiment, the invention includes a paper product including a paper substrate comprising a web of fibers having a first surface and a second surface and having a selective indicator provided over the first surface, the first surface observably different than the second surface under a selective condition. A first release coating can be provided over the first surface or the second surface. In an embodiment, the invention includes a method for forming a paper product comprising applying a composition having a selective indicator to a web of fibers having a first surface and a second surface, wherein the composition is applied to the first surface and results in the first surface being observably different under a selective condition. The method further includes applying a first release composition to one of the first surface or second surfaces to form the paper product.

DETAILED DESCRIPTION

Release liners refer to those sheet products that exhibit release properties so that they can pull away from a substrate in a manner so as to preserve desired properties of the substrate. By way of example, tape generally has an adhesive provided on one or both of it sides. If the adhesive is not protected before end use, its adhesive qualities may be diminished and the product may be difficult to handle. A release liner can be provided over the adhesive on the tape having release properties that allows the release liner to be pulled off while preserving the desired adhesive properties of the tape.

There are different types of release liners including one-sided release liners, two-sided release liners, and differential release liners. One-sided release liners are treated to have desired release properties on one side and two-sided release liners are treated to have desired release properties on both sides. Differential release liners are treated to have desired release properties on both sides but the release properties of the two sides are different from one another. As one side of a release liner can be different from the other side, there is a need for a way of distinguishing between the two sides.

Embodiments of the invention include release liners with selective indicators provided on one side such that the two sides of the release liner are observably different under selective conditions. Embodiments of the invention include methods of making release liners with selective indicators provided on one side such that the two sides of the release liner are observably different under selective conditions. In an embodiment, the selective indicator is an optical brightener and the selective condition is the application of UV light.

As used herein, the term “provided over” refers to a spatial relationship between two components. When one component is “provided over” another, they may be touching, immediately adjacent, or there may be other components disposed in between.

As used herein, the term “provided on” also refers to a spatial relationship between two components. When one component is “provided on” another, they are touching or immediately adjacent without other components disposed in between.

As used herein, the term “observably different” refers to differences that can be distinguished upon observation with the naked eye.

As used herein, the term “release properties” in reference to a release liner includes aspects such as the release force for the release liner as measured in units of g/in and determined according to TAPPI Useful Method #502. One of skill in the art will appreciate that even where two release liner coatings have equivalent release force, their release properties can still be different as a result of the texture of the release liner coating, the texture of the paper substrate underlying the release liner coating, or both.

As used herein, the term “selective conditions” refers to conditions other than ambient conditions that are applied for the purpose of distinguishing between the sides of a release liner. Selective conditions may include levels and types of light (such as UV light), moisture, pressure, sound, and the like provided at levels other than at ambient levels. A specific example of the application of a selective condition would be the application of UV light at a level other than at ambient levels.

As used herein, the term “selective indicator” refers to a compound or composition that can be applied to a paper product and can be detected visually under selective conditions. For example, a selective indicator provided on one side of a paper product but not the other can result in the two sides of the paper being observably different under selective conditions. A specific example of a selective indicator is an optical brightener.

Manufacture of the Paper Product

Referring to FIG. 1, a process for making a paper product according to the invention is shown at reference numeral 10. It should be understood that FIG. 1 is an exemplary schematic diagram and includes many of the operations carried out in commercial paper making facilities. The equipment used in a particular operation may vary from facility to facility, but it is expected that the same general operations will be present.

The starting material 12 generally includes pulp 14. The wood pulp can include a blend of hard wood and soft wood fibers. The wood pulp can be provided as cellulose fiber from chemical pulped wood, and can include a blend from coniferous and deciduous trees. Blends of hardwood and softwood fibers are frequently used. The fibers can also be bleached or unbleached. One of skill in the art will appreciate that the bleaching can be accomplished through many methods including the use of chlorine, hypochlorite, chlorine dioxide, oxygen, peroxide, ozone, or a caustic extraction. The fibers may also comprise other types of natural fibers or synthetic fibers as described more fully below. The starting material 12 may also include post-consumer waste fiber. Post-consumer waste fiber is recovered from paper that is recycled after consumer use. By way of example, the starting material 12 may include at least 10% post-consumer waster fiber. The starting material 12 may include fibers from various sources as described in greater detail below.

The starting material 12 can be processed through a refining operation 16 and through a cleaning and screening operation 18. The cleansed pulp 20 can be applied through a head box 22 onto a fourdrinier machine 24 to create a web of fibers 26. The side of the web of fibers 26 facing down on the fourdrinier machine 24 is known as the “wire side.” The side of the web of fibers 26 facing up on the fourdrinier machine 24 is known as the “felt side.” Certain additives can be added at or before the head box 22 and this is referred to as “wet end chemistry.”

Wet end additives can be provided for strength, opacity, etc. Exemplary wet strength additives include urea-formaldehyde, melamine-formaldehyde, and polyamide. Exemplary dry strength additives include starches (such as cationic potato starch). One of skill in the art will appreciate that many different types of starches can be used such as corn starch, rice starch, tapioca starch, and wheat starch. Exemplary opacifying additives include kaolin clays, titanium dioxide, and calcium carbonate. One of skill in the art will appreciate that these components may be added in many different ways including being added as a part of a batch control process or being added through a metering system for continuous operations. Other components, such as defoaming agents, pitch dispersants, plasticizers (urea), etc. may also be added prior to the head box 22. Acid alum (aluminum sulfate and sulfuric acid) may be added prior to the head box 22. Acid alum can serve various purposes including drainage enhancement, rosin sizing, part of certain retention aid programs, dye fixation, cationic source, acidic buffer. Sizing agents that increase water hold-out are also sometimes added as a part of wet end chemistry.

The web of fibers 26 can be considered continuous in the machine direction. The web of fibers 26 can be processed through a wet press section 28 to remove water, and then through a first drier section 30 to further reduce the water content and provide an intermediate paper substrate 32.

The intermediate paper substrate 32 is then processed through a size press 34 wherein a size press composition is applied to the surfaces of the intermediate paper substrate 32. Certain additives can be added to the size press composition and this is referred to as “size press chemistry.”

Size press additives can be provided for sizing, strength, to close up the surface of the sheet (film formers such as starch, polyvinyl alcohol, sodium alginate, latex, etc.), to fill in the surface of the sheet, for water resistance, and/or oil resistance. Exemplary water resistance additives include alkyl ketene dimmer (AKD), styrene maleic anhydride (SMA), and waxes. Exemplary oil resistance additives include fluorochemicals. Exemplary fillers include kaolin clays, titanium dioxide, and calcium carbonate. Plasticizers may also be added at the size press 34. Plasticizers include humectants and can function to keep paper soft and make it less likely that the paper will fracture. Suitable plasticizers include urea, nitrates, glycerine, and saccharides (such as NEOSORB®, available from Roquette Corp., Gurnee, Ill.). Selective indicators can also be applied at the size press. However, selective indicators can also be applied at other points in the paper making process.

The size press 34 can be configured to apply a first size press composition to the wire side of the intermediate paper substrate 32 and a second, different, size press composition to the felt side of the intermediate paper substrate 32. A selective indicator can be added to one of the size press compositions. By way of example, an optical brightener can be added to one of the size press compositions. Exemplary optical brighteners include diamino stilbene, diethanol amine, or diisopropanol amine. Accordingly, after the size press 34 the intermediate paper substrate 32 has a selective indicator, such as an optical brightener, disposed on one side but not the other. The optical brightener may penetrate into the intermediate paper substrate 32 to a degree. However, in an embodiment, the optical brightener does not penetrate into the intermediate paper substrate 32. After the optical brightener is applied, the two sides can be easily distinguished by the naked eye upon shining a UV lamp or “blacklight” on the paper substrate 32.

It will be appreciated that are also other means of applying components besides applying them at the size press 34. Other application technologies including roll coaters, gate-roll coaters, blade coaters, metering size presses, bill blade coater, and sprayers may also be used to apply components to the intermediate paper substrate 32 as a part of the paper making machine (“on machine”) or as a part of a procedure entirely separate from the paper making machine (“off machine”). By way of example, otherwise finished paper may be unrolled and then fed through a separate machine to apply a specific component.

The intermediate paper substrate 32 is then dried in a second drier section 38. The intermediate paper substrate 32 can either be machine finished, machine calendered, or calendered in a super-calender 40 to provide a semi-finished paper substrate 42. The semi-finished paper substrate 42 can then be sent to a winder and put on a roll 52. When put on a roll 52, the semi-finished paper substrate 42 can be referred to as roll stock.

At this point, the roll stock can be sold or can simply be fed into a further line for further processing. In an embodiment, a release liner coating is applied to the semi-finished paper substrate 42 to form a release liner product 58.

Referring now to FIG. 2, a diagrammatic view of an exemplary release liner application process according to the invention is shown. The process starts with unwinding semi-finished paper substrate 42 off of a roll 52. The semi-finished paper substrate 42 is then fed through one or more presses (54 and 56) to apply a release liner coating composition to one or both sides of the semi-finished paper substrate 42. In an embodiment, a different release liner coating composition is applied to one side of the semi-finished paper substrate 42, than to the other. In an embodiment, the same release liner coating composition is applied to both sides of the semi-finished paper substrate 42 but applied in different ways resulting in different release properties between each side. In some embodiments, the semi-finished paper substrate 42 is then subjected to a curing process 60 in order to cure components of the release liner coating composition and create a release liner product 58. The curing process 60 may include the application of heat, UV radiation, or other processes depending on the content of the release liner coating composition being applied.

In an embodiment, one side of the resulting release liner product 58 has different release properties than the other side. As a selective indicator, such as an optical brightener, was previously applied to the semi-finished paper substrate 42 on only one side, the two sides of the release liner product 58 having different release properties can be distinguished. The selective indicator may be provided on either side of the release liner. In an embodiment, a single sided release liner is provided and the selective indicator is on the opposite side as the release liner coating. In an embodiment, a single sided release liner is provided and the selective indicator is on the same side as the release liner coating. In an embodiment, a differential release liner is provided and the selective indicator is provided on the side having lower release force. In an embodiment, a differential release liner is provided and the selective indicator is provided on the side having greater release force.

The selective indicator, such as an optical brightener, described as being added as a part of size-press chemistry above may alternately be mixed with one of the release liner coating compositions. However, as optical brighteners generally capture UV light, the optical brightener may interfere with the curing process 60 if curing is triggered by UV light. Accordingly, in an embodiment, the optical brightener is not mixed with the release liner coating composition. After the curing process, the release liner product 58 is either further processed, such as by cutting the release liner product 58 into smaller dimensions, or it is then rolled onto a release liner product roll 62 for storage or shipment.

Referring now to FIG. 3, a schematic cross-sectional view of a differential release liner 100 in accordance with the invention is shown. A web of fibers 102 has a first side 104 and a second side 106. A selective indicator, such as an optical brightener 108, is provided on the second side 106 of the web of fibers 102. As shown, the optical brightener 108 may absorb into the web of fibers 102 to a degree. However, in other embodiments, the optical brightener 108 may not absorb into the web of fibers 102. The optical brightener can be on either the first side or the second side. The brightening effect of the optical brightener 108 will be significantly viewable from one of the two sides. Therefore, the side of the web of fibers that has the optical brightener 108 can be readily distinguishable with the naked eye from the side of the web of fibers that does not have the optical brightener when viewed under selective conditions, such as UV light.

A first release coating 110 is provided over the first side 104. A second release coating 112 is provided over the second side 106. The first and second release coatings provide different release properties. In some embodiment, the first and second release coatings can have different release forces. In some embodiments, the first and second release coatings may have equivalent release forces but still have different release properties. For example, the release forces (g/in) between the two sides may be equivalent when measured with respect to TAPPI useful method #502 but the release properties may be different because of different underlying texture between the wire side and the felt side of the web of fibers.

Optical Brighteners

The term “optical brightener” may also be referred to as a “fluorescent whitening agent” and as used herein refers to compounds that absorb ultraviolet light and re-emit light in the blue region.

As discussed above, optical brighteners can be disposed on one side of the paper substrate. In an embodiment, optical brighteners are added to one of the size press compositions. Using more optical brightener than is necessary may be inefficient. In an embodiment, the size press composition contains less than 5.0% of an optical brightener based on solids. Using too little of an optical brightener may make it difficult to distinguish between the sides of the release liner product. In an embodiment, the size press composition contains more than 0.05% of an optical brightener based on solids. In an embodiment, the size press composition contains between about 0.5% to 2.0% of an optical brightener based on solids. In an embodiment, one of the size press compositions contains 1.25% of the optical brightener based on solids, or approximately 0.125% optical brightener based on volume. However, it will be appreciated that the precise amounts of the optical brightener used in the size press composition can be varied depending on how much of the size press composition is being applied. For example, if it is desired to provide a certain total amount of optical brightener onto the paper substrate, this can be achieved either by using a greater amount of a size press composition having a lower concentration of optical brightener or by using a lesser amount of a size press composition having a greater concentration of optical brightener. Moreover, the precise concentration of optical brightener used will also depend on where it is applied to the paper substrate during the manufacturing process, whether or not it is absorbed into the paper substrate, the specific chemical compound used as an optical brightener, etc.

Optical brighteners used in the present invention may include stilbene derivatives, such as bistriazinyl derivatives of 4,4′-diaminostilbene-2,2′-disulfonic acid, examples include CAS Registry Numbers 17118-48-8, 31900-04-6, 17118-46-6, 17118-44-4, 32466-46-9, 17863-51-3, 16470-24-9, 17118-40-0, and 41098-56-0; styryl derivatives of benzene and biphenyl, such as CAS Registry Numbers 13001-39-3 and 27344-41-8; pyrazolines, such as CAS Registry Numbers 2697-84-9, 2744-49-2, 38848-70-3, 27441-70-9, and 6608-82-8; bis(benzoxazol-2-yl) derivatives, such as CAS Registry Numbers 1041-00-5, 1533-45-5, 5089-22-5, and 2866-43-5; coumarins, such as CAS Registry Numbers 305-01-1, 90-33-5, 26093-31-2, and 87-01-4; carbostyrils, such as CAS Registry Number 33934-60-0; and other heterocyclic systems such as naphthalimides.

In an embodiment, the optical brightener composition includes a diamino stilbene. In an embodiment, the optical brightener composition includes diethanolamine. In an embodiment, the optical brightener composition includes diisopropanol amine.

Optical brighteners are widely available commercially such as LEUCOPHOR® available from Clariant Corporation, Charlotte, N.C., TINOPAL® available from Ciba Specialty Chemicals, Suffolk, Va., and BLANKOPHOR® available from Lanxess (formerly Bayer), Pittsburgh, Pa.

Paper Substrate

Refining is the treatment of pulp fibers to develop their papermaking properties. Refining increases the strength of fiber to fiber bonds by increasing the surface area of the fibers and making the fibers more pliable to conform around each other, which increases the bonding surface area and leads to a denser sheet, with fewer voids. Most strength properties of paper increase with pulp refining, since they rely on fiber to fiber bonding. The tear strength, which depends highly on the strength of the individual fibers, actually decreases with refining. Refining of pulp increases the fibers flexibility and leads to denser paper. This means bulk, opacity, and porosity decrease (porosity values increase) with refining. Fibrillation is a result of refining paper fibers. Fibrillation is the production of rough surfaces on fibers by mechanical and/or chemical action; refiners break the outer layer of fibers, i.e., the primary cell wall, causing the fibrils from the secondary cell wall to protrude from the fiber surfaces.

The extent to which a paper product is made with refined fibers can be measured through several means. One type of testing for refined fibers is referred to as freeness testing. In this mode of testing, the speed with which water drains through a sample piece of paper is measured. Because paper made with highly refined fibers has fewer voids and small holes, it takes water longer to drain through a sheet of paper made with highly refined fibers. A standard for this mode of testing is the Canadian Standard Freeness (CSF) test. The CSF test was developed for use with groundwood pulps and was not intended for use with chemical pulps; nevertheless, it is the standard test for monitoring refining in North American mills. TAPPI (Technical Association of the Pulp and Paper Industry) standard test T 227 corresponds to the CSF test. Another common test of the refined nature of paper is the Shopper Riegler test, which is similar in concept to the CSF test.

In an embodiment, fibers are used that have a Canadian Standard Freeness of greater than about 50 cm³. Less refined paper has more voids and holes and this may lead to increased penetration of surface treatments. In an embodiment, fibers are used that have a freeness of less than about 500 cm³. In some embodiments of the invention, the web of fibers is made with fibers having a Canadian Standard Freeness of about 50 cm³ to about 500 cm³.

The finished paper substrate refers to the web of fibers and additives from both wet end chemistry and size press chemistry. In general, any weight of paper may be used in accordance with the present invention. Therefore, the finished paper substrate is made in weights desired by end users. However, using a paper substrate that is heavier than necessary for a particular application may not be economically efficient. In an embodiment, the finished paper substrate is less than about 120 pounds per 3000 ft² of paper. Paper that is too low in weight may not be suitable for use as a release liner. In an embodiment, the finished paper substrate is greater than about 30 pounds per 3000 ft² of paper. The finished paper substrate of the invention may be in the range of about 30 to 120 pounds per 3000 ft² of paper.

One of skill in the art will appreciate that the web of fibers can comprise many different types of fibers, both natural and synthetic. Exemplary natural fibers that can be used include wood fibers and non-wood natural fibers such as vegetable fibers, cotton, various straws (wheat, rye, and others), various canes (bagasse and kenaf), grasses (bamboo, etc.), hemp, corn stalks, etc. Exemplary synthetic fibers include polyester, polypropylene, polyethylene, rayon, nylon, acrylic, glass, and the like.

The fibers used in the invention can be extracted with various pulping techniques. For example, mechanical or high yield pulping can be used for stone groundwood, pressurized groundwood, refiner mechanical pulp, and thermomechanical pulp. Chemical pulping can be used incorporating kraft, sulfite, and soda processing. Semi-chemical and chemi-mechanical pulping can also be used which includes combinations of mechanical and chemical processes to produce chemi-thermomechanical pulp.

The pulp used for creating the web of fibers can include a blend of hardwood and softwood fibers. The pulp can be provided as cellulose fiber from chemical pulped wood, and can include a blend from coniferous and deciduous trees. By way of example, the fibers can be from Northern hardwood, Northern softwood, Southern hardwood, or Southern softwood. Hardwood fibers tend to be more brittle but are generally more cost effective for use because the yield for pulp from hardwood is higher than the yield for pulp from softwood. In an embodiment, the pulp contains from about 0 to about 70% hardwood fibers. Softwood fibers have better paper making characteristics but are more expensive. In an embodiment, the pulp contains from about 0 to about 70% softwood fibers. In an embodiment, the pulp contains a blend of hardwood and softwood fibers.

The pulp can also include post-consumer waste (PCW) fiber. Post-consumer waste fiber is recovered from paper that is recycled after consumer use. Post-consumer waste fiber can include both natural and synthetic fiber. Incorporation of PCW fiber can aid in efficient use of resources and increase the satisfaction of the end user. In an embodiment, the pulp includes at least 10% PCW fiber. In another embodiment, the pulp includes at least 20% PCW fiber. In still another embodiment, the pulp includes at least 30% PCW fiber. PCW fiber may not have the same strength characteristics as virgin cellulose fiber and may be more expensive to incorporate. In an embodiment, the pulp includes at least 10% PCW fiber but less than 50% PCW fiber. In another embodiment, the pulp includes at least 20% PCW fiber but less than 40% PCW fiber.

Release Liner Coating

The release liner coating may include any of a variety of components. In an embodiment, the release coating composition comprises at least one material chosen from the group consisting of: alkoxysilane silicones, acetoxysilane silicones, silanol silicones, epoxy silicones, and vinyl silicones, and preferably comprises silanol-terminated silicones. By way of example, the release liner coating composition can include a silicone composition. In an embodiment, the release liner coating composition includes a polyorganosiloxane, such as polydimethylsiloxane.

If too small of an amount of release coating is applied, the paper substrate may not have the desired release properties. In some embodiments, at least 0.1 lbs/3000 ft² of release coating is applied to a particular side of the paper substrate. Having too much release coating may be economically inefficient. In an embodiment, less than 2.0 lbs/3000 ft² of release coating is applied to a particular side of the paper substrate. In an embodiment, about 0.4 lbs/3000 ft² to about 1.3 lbs/3000 ft² of the release coating is applied. In an embodiment of the invention, a combined amount of about 0.6 lbs/3000 ft² of the release liner coating is applied to the paper substrate including both sides (measured as the amount of solids applied).

A wide variety of polyorganosiloxanes (commonly called silicones) can be used in the practice of the invention. Such polyorganosiloxanes are also sometimes referred to as polymeric silicone resins, rubbers, oils or fluids. These compositions are well known and fully described in the literature. These compositions are comprised essentially of silicon atoms connected to each other by oxygen atoms through silicon-oxygen linkages, such as:

wherein each R is an organic group, generally an alkyl group. In an embodiment, the compositions used in the practice of the invention are high molecular weight polymers and copolymers having molecular weights in the range of 5,000 to 250,000. Exemplary polyorganosiloxane materials that can be used in forming the release liner coating of the present invention include those disclosed in U.S. Pat. Nos. 2,258,218; 2,258,220; 2,258,222; 2,494,920; 3,432,333; and 3,518,325; the contents of which are herein incorporated by reference.

The silicone release compositions can be applied as solutions in organic solvents, as emulsions in water, or in 100% solids form (solvent-less). Many different organic solvents can be used. In an embodiment, hexane is used to form the release liner coating composition. In an embodiment, any organic solvent having a boiling point equal to or less than that of xylene (approximately 137-140° C.) can be used. Higher boiling solvents can be used but may be less economical. In a particular embodiment, hexane is used as a solvent to form a solution of a release liner composition that is disposed on one side of the paper product while a water and release liner composition emulsion is formed and disposed on the other side of the paper product.

The release liner coating composition can be applied to the substrates by any conventional means known in the coating art such as gravure, reverse gravure, offset gravure, roller coating, curtain coating, brushing, spraying, knife-over roll, metering red, reverse roll coating, doctor knife, dipping, die coating, etc.

In some embodiments of the invention, the release liner coating compositions may be thermally cured or radiation cured after application to the web of fibers. In an embodiment, the thermally curable compositions comprise at least one polyorganosiloxane and at least one catalyst or curing agent for such polyorganosiloxane(s). Such compositions may also contain at least one cure accelerator and/or adhesivity promoter (sometimes referred to as an anchorage additive). The amount of curing agent or catalyst, cure accelerator and/or adhesivity promoter employed in the silicone release coatings of the invention can be varied widely depending upon the curing temperature, the particular catalyst used, the particular polyorganosiloxane materials selected, the particular cure accelerator and/or adhesivity promoter used, the substrate, desired curing time, etc. In an embodiment, the amount of any of such components is in the range of 0.5 to 20 weight percent of the silicone material employed.

Suitable catalysts that can be employed in the curing of the release liner coating compositions of the invention include various compounds containing metals such as tin, lead, platinum, rhodium, etc. Specific examples of catalysts include: dibutyl tin diacetate, dibutyl tin di-ethylhexanoate, dihexyl tin di-2-ethyl hexanoate, ethyl tin trihexanoate, dibutyl tin dilaurate, octadecyl tin dilaurate, dibutyl tin diacetate, tri-butyl tin acetate, dibutyl tin succinate, various lead salts such as lead naphthenate and lead octoate, zinc octoate, zinc stearate, iron octoate, various organic peroxides such as benzoyl peroxide and 2,4-dichlorobenzoyl peroxide; and others well known in the art as curing agents or catalysts for polyorganosiloxane (silicone) materials. Other catalysts include the carboxylic acid salts of organolin compounds containing at least one carbon-tin bond such as those previously mentioned. Metal complexes of platinum and rhodium are also useful. Amines and amines derivatives such as diethylene triamine, triethylene tetramine and ethanol amine, as well as amine precursors such as the isoeyanate compounds and amine-functional silanes such as gamma-aminopropyl triethoxy silane can also be used as curing catalysts. The amine salts of carboxylic acids can also be used as curing agents in the silicon release liner coatings of the invention.

The cure accelerators and/or adhesivity promoters which can be used in the silicone release coating, are also well known in the art. Exemplary of such cure accelerators and/or adhesivity promoters are amines, amine-functional silanes and amine precursors previously discussed as well as other silane derivatives and orthosilicates such as tetra(diethylene glycol monomethyl ether) silane. Isocyanate compounds of the invention include any isocyanate which is soluble in organic solvents and which has an average of at least two isocyanate groups per molecule. Such isocyanates can be monomeric or polymeric in nature, e.g., the isocyanate can be a partially hydrolyzed toluene diisocyanate. Other such isocyanates include the reaction products of an isocyanate with a polyhydroxyl compound (i.e., a polyurethane or allophanates derived therefrom), the reaction product of an isocyanate and or catalyst used in conjunction with said silicone material.

For practical continuous operations the time required for curing at room temperature is generally too long. Most curing agents or catalysts are capable of promoting relatively rapid curing at moderate elevated temperatures. The temperature at which relatively rapid curing takes place is sometimes referred to as the curing initiating temperature even though curing will take place at room temperature. In an embodiment, this temperature is in the range of 160° F. to 650° F. Once curing has been initiated and maintained at an elevated temperature for a short period of time as described herein, the curing can then advantageously be allowed to proceed by aging at reduced temperatures, e.g., at room temperatures or moderately (25° F. to 50° F.) above. The choice of temperature actually employed in the curing steps will depend upon a number of factors such as the type of silicone coating material used, the curing catalyst used with said silicone material, and the rate at which the coated substrate is passed through the heating zone.

The release liner coating composition can also include radiation-curable compositions. By way of example, radiation-curable organopolysiloxanes can be cured by ultraviolet or electron beam radiation with or without the assistance of a photoinitiator such as benzophenone. One type of organopolysiloxane that is useful in preparing release coatings contains acryloxy groups, methacryloxy groups, or mixtures thereof. A variety of acryloxy or methacryloxy containing organopolysiloxanes are known and can be used for release coatings. The siloxanes containing the acryloxy or methacryloxy groups can be prepared, for example, by reacting a siloxane containing hydroxyl groups or epoxy groups with acrylic acid or methacrylic acid. The siloxanes containing hydroxyl groups may be prepared by reacting a reactive siloxane (e.g., containing halogen) with a polyhydroxy compound such as ethylene glycol, propylene glycol, glycerol or pentaerythritol.

Various methods for producing organopolysiloxanes are known. The disclosures of U.S. Pat. Nos. 3,878,263; 4,064,286; 4,301,268; 4,306,050; 4,908,274; 4,963,438; 4,978,726; and 5,034,491 are hereby incorporated by reference for their disclosure of acrylate or methacrylate containing organopolysiloxanes and methods of preparing organopolysiloxanes containing acryloxy and/or methacryloxy groups useful in the compositions of the present invention.

The radiation-curable release compositions of the present invention optionally may contain at least one photoinitiator. A photoinitiator may be incorporated into the curable release compositions when compositions are to be cured by exposure to non-ionizing radiation such as ultraviolet light. Photoinitiators are not required when the curable silicone is cured by electron beam radiation. Examples of photoinitiators which may be used in combination with ultraviolet light includes, for example, benzyl ketals, benzoin ethers, acetophenone derivatives, ketoxime ethers, benzophenone, benzo or thioxanthones, etc. Specific examples of photoinitiators include: 2,2-diethoxyacetophenone; 2- or 3- or 4-bromoacetophenone; benzoin; benzophenone; benzoquinone; 1-chloroanthroquinone; p-diacetyl-benzene; 9,10-dibromoanthracene; 1,3-diphenyl-2-propanone; 1,4-naphthyl-phenyl ketone; 2,3-pentenedione; propiophenone; chlorothioxanthone; xanthone; and mixtures thereof.

The above specification provides a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. 

1. A paper product comprising: a paper substrate comprising a web of fibers having a first surface and a second surface and having a selective indicator provided over the first surface, the first surface observably different than the second surface under a selective condition; and a first release coating provided over the first surface or the second surface.
 2. The paper product of claim 1, further comprising a second release coating provided over the surface opposite the first release coating.
 3. The paper product of claim 2, wherein the paper product comprises a differential release liner.
 4. The paper product of claim 1, wherein the selective indicator is provided on the first surface.
 5. The paper product of claim 1, wherein the selective condition comprises UV light.
 6. The paper product of claim 1, wherein the selective indicator is an optical brightener.
 7. The paper product of claim 1, the optical brightener comprising at least one of stilbene derivatives, styryl derivatives of benzene and biphenyl, pyrazolines, bis(benzoxazol-2-yl) derivatives, coumarins, carbostyrils, and naphthalimides.
 8. The paper product of claim 1, the optical brightener comprises diamino stilbene, diethanolamine, or diisopropanol amine.
 9. The paper product of claim 1, the optical brightener comprising a stilbene derivative.
 10. The paper product of claim 1, the optical brightener comprising diamino stilbene.
 11. The paper product of claim 1, the first release coating comprising a polyorganosiloxane.
 12. The paper product of claim 11, the first release coating comprising polydimethyl siloxane.
 13. The paper product of claim 2, the second release coating comprising a polyorganosiloxane.
 14. The paper product of claim 13, the second release coating comprising polydimethyl siloxane.
 15. The paper product of claim 2, the first and second release coatings comprising a combined amount of about 0.6 lbs. per 3000 ft².
 16. The paper product of claim 1, wherein the web of fibers has a weight of between 30 lbs./3,000 ft.² and 120 lbs./3,000 ft.².
 17. The paper product of claim 1, wherein the web of fibers has a Canadian Standard Freeness value of between about 50 cm³ and 500 cm³ according to TAPPI test T
 227. 18. A method for forming a paper product comprising: (a) applying a composition comprising a selective indicator to a web of fibers having a first surface and a second surface, wherein the composition is applied to the first surface and results in the first surface being observably different under a selective condition; and (b) applying a first release composition to one of the first surface or second surfaces to form the paper product.
 19. The method of claim 18, further comprising applying a second release composition to the surface opposite the surface that the first release composition was applied to.
 20. The method of claim 19, wherein the paper product comprises a differential release liner.
 21. The method of claim 18, the selective condition comprising UV light.
 22. The method of claim 18, the selective indicator comprising an optical brightener.
 23. The method of claim 22, the optical brightener comprising at least one of stilbene derivatives, styryl derivatives of benzene and biphenyl, pyrazolines, bis(benzoxazol-2-yl) derivatives, coumarins, carbostyrils, and naphthalimides.
 24. The method of claim 22, the optical brightener comprising diamino stilbene, diethanolamine, or diisopropanol amine.
 25. The method of claim 22, the optical brightener comprising a stilbene derivative.
 26. The method of claim 22, the optical brightener comprising diamino stilbene.
 27. The method of claim 18, the first release composition comprising a polyorganosiloxane.
 28. The method of claim 18, the first release composition comprising polydimethyl siloxane.
 29. The method of claim 19, the second release composition comprising a polyorganosiloxane.
 30. The method of claim 19, the second release composition comprising polydimethyl siloxane.
 31. The method of claim 19, wherein the first and second release coatings are applied in amounts to result in a combined release liner coating weight of about 0.6 lbs. per 3000 ft².
 32. The method of claim 18, wherein the web of fibers has a weight of between 30 lbs./3,000 ft.² and 120 lbs./3,000 ft.².
 33. The method of claim 19, wherein the web of fibers has a Canadian Standard Freeness value of between about 50 cm³ and 500 cm³ according to TAPPI test T
 227. 34. A method for forming a paper product comprising: applying a first release composition to a surface of a web of fibers to form a paper product, the web of fibers having first and second surfaces, the web of fibers having a selective indicator provided on or provided over the first or second surface so that the first surface and the second surface are observably different under a selective condition.
 35. The method of claim 34, further comprising applying a second release composition to the surface opposite the surface that the first release composition was applied to.
 36. The method of claim 34, wherein the paper product comprises a differential release liner.
 37. The method of claim 34, the selective condition comprising UV light.
 38. The method of claim 34, the selective indicator comprising an optical brightener.
 39. The method of claim 38, the optical brightener comprising at least one of stilbene derivatives, styryl derivatives of benzene and biphenyl, pyrazolines, bis(benzoxazol-2-yl) derivatives, coumarins, carbostyrils, and naphthalimides.
 40. The method of claim 38, the optical brightener comprising diamino stilbene, diethanolamine, or diisopropanol amine.
 41. The method of claim 38, the optical brightener comprising a stilbene derivative.
 42. The method of claim 38, the optical brightener comprising diamino stilbene.
 43. The method of claim 34, the first release composition comprising a polyorganosiloxane.
 44. The method of claim 34, the first release composition comprising polydimethyl siloxane.
 45. The method of claim 35, the second release composition comprising a polyorganosiloxane.
 46. The method of claim 35, the second release composition comprising polydimethyl siloxane.
 47. The method of claim 35, wherein the first and second release coatings are applied in amounts to result in a combined release liner coating weight of about 0.6 lbs. per 3000 ft².
 48. The method of claim 34, wherein the web of fibers has a weight of between 30 lbs./3,000 ft.² and 120 lbs./3,000 ft.².
 49. The method of claim 34, wherein the web of fibers has a Canadian Standard Freeness value of between about 50 cm³ and 500 cm³ according to TAPPI test T
 227. 